HP StorageWorks Storage Mirroring for Linux User's Guide (T2558-96078, February 2008)
11 - 2
Failover Terminology
Missed Packets—The missed packets is the configurable setting that specifies how many monitor replies can be missed
before assuming the source machine has failed.
Monitored IP Addresses—Monitored IP addresses are the IP addresses on the source selected to be monitored by a
Storage Mirroring target.
Monitor Interval—The monitor interval is the configurable setting that specifies how often the monitor request is sent
to the source machine.
Monitor Reply—A monitor reply is the acknowledgement that the source sends to the target indicating that it is still
online.
Monitor Request—A monitor request is an inquiry sent from the target to the source to determine if the source is still
active.
Timeout—The failover timeout is the amount of time before failover begins. The time is calculated by multiplying the
values of the monitor interval and missed packets settings. This time is displayed on the Failover Control Center.
Unmonitored IP Addresses—On a machine with multiple IP addresses, Storage Mirroring will not monitor the IP
addresses that are not selected, but the target can assume these addresses during failover, if configured.
How Failover Works
1. The target machine monitors the source machine and waits for a failure.
2. A source failure is detected and the failover process begins. (For more information on failure detection, see How Failure
Detection Works
on page 11-4.)
3. If specified, a pre-failover script executes on the target. This script is user-defined and optional. Scripts may be used to
stop daemons on the target that will not be needed or may be in conflict after the target stands in for the failed source.
Scripts can also send network messages notifying administrators that failover is about to occur.
NOTE: Until the failover process has completed executing, user and application requests destined for the source
machine will not be delivered.
User and application requests are sent to
Source Name: Marketing
IP Address: 125.7.82.43
Target Name: Backup
IP Address: 125.7.82.67
Monitor Requests
and Replies
the source by locating the IP address
Failed Source
Target Name: Backup
IP Address: 125.7.82.67
Failover Script
User and application momentarily wait
while failover occurs